SuperTIGER ultra-heavy galactic cosmic ray atmospheric corrections using Geant4 simulations

SuperTIGER (Super Trans-Iron Galactic Element Recorder) is a balloon-borne instrument designed to directly measure ultra-heavy Galactic cosmic-ray (UHGCR) nuclei. SuperTIGER had two successful Antarctic flights: SuperTIGER-1 in 2012 for 55 days, and SuperTIGER-2 in 2019 for 32 days. Stratospheric float altitudes varied between ∼ 36 – 40 km for the flights. To obtain top-of-atmosphere (TOA) abundances, the observed abundance measurements must be corrected for propagation through the residual ∼ 0.5% of atmosphere and inactive detector material. The approach developed for the previous TIGER instrument propagates TOA elemental abundances from satellite measurements down through the atmosphere to flight altitudes, accounting for gains and losses due to charge-changing nuclear interactions. Final TOA abundances are found by iteratively adjusting the assumed TOA abundances in the propagation model until the model produces instrument abundances that match the flight measurements. We develop a new method to obtain TOA abundances of UHGCR nuclei by simulating nuclear interactions and energy losses cosmic-ray nuclei experience propagating through the atmosphere using Geant4. We simulate a slab of atmosphere material as well as instrument material above the active detector and record energy loss and nuclear interactions of Galactic cosmic ray (GCR) projectiles. Results from these simulations are used to create a response matrix to describe the charge-changing losses or gains of cosmic-ray nuclei species. The simulation results are also used to obtain required TOA energy for cosmic-ray nuclei to trigger SuperTIGER’s acrylic Cherenkov detector (320 MeV/nuc). We compare the TOA energy and TOA abundances from simulation-based corrections to previous analytical corrections.